The most important thing to keep in mind is that the adults are paying $38.99, and the young children are paying only $10.99 (even if you're getting
free dining, these dollar amounts still apply to what you're going to get). Smaller portion sizes alone cannot account for how incredibly inexpensive the Dining Plan is for young children. So in addition to smaller portion sizes, there are very few choices. That accounts for the much-lower price. I believe that as long as you keep that comparison in mind ($38.99 versus $10.99) the differences will make sense to you. If the price difference doesn't matter you don't want your child having more limited choices with relatively less special meals, then don't get the Dining Plan.
Here's a link to the Dining Plan FAQ, which explains the basics of the Dining Plan including how it applies to young children:
http://www.disboards.com/showpost.php?p=16079998
As you can see, children are entitled to entree, dessert and beverage at their CS meals; their own appetizer, entree, dessert and beverage at TS meals. And also, their own snacks, and there is no difference between the snacks available to young children and the snacks available to adults. The difference with regard to CS meals and TS meals, besides smaller portion sizes, is more basic and less sophisticated food choices, and often the same choices from eatery to eatery, while adults are offered more variety and choice.